Pipe separator with improved separation

ABSTRACT

A pipe separator for separation of fluids, for example separation of oil, gas and water in connection with the extraction and production of oil and gas from formations under the sea bed. It comprises an extended, tubular separator body ( 1 ) that has a diameter at the inlet and outlet ends that is mainly equal to or slightly greater than the diameter of the transport pipe to which the separator body is connected. A cyclone ( 3 ) is arranged upstream of the separator body for separation of any gas present. An electrostatic coalescer ( 4 ) is incorporated in and constitutes an integrated part of the separator body ( 1 ).

The present invention concerns a pipe separator for separation offluids, for example separation of oil, gas and water in connection withthe extraction and production of oil and gas from formations under thesea bed, comprising an extended, tubular separator body that has adiameter at the inlet and outlet ends that is mainly equivalent to thediameter of the transport pipe to which the pipe separator is connected,a cyclone arranged upstream of the separator body for separation of anygas present and an electrostatic coalescer arranged in connection withthe pipe separator.

The applicant's own Norwegian patent application nos. 19994244,20015048, 20016216, 20020619 and 20023919 describe prior art pipeseparators for the separation of oil, water and/or gas downhole, on thesea bed or on the surface, on a platform or similar. In particular,patent application no. 20023919 shows a solution in which a separate,compact electrostatic coalescer is used in connection with the pipeseparator. The oil flow from the pipe separator is passed to thecoalescer downstream of the pipe separator and subsequently to a furtheroil/water separator that removes the remaining water after separation inthe pipe separator. This prior art solution is particularly designedfor, but not limited to, medium heavy oils with water removal from theoil phase to 0.5% water, using a cyclone or other type of gas/liquidseparator to remove gas before the pipe separator.

The solution requires an additional separator, which is complicated andexpensive, and the coalescer itself, which is of a vertical type, cannotbe reamed or pigged (cleaned) in the conventional manner. This alsorepresents a considerable disadvantage of the prior art solution.

The present invention represents a considerably simplified separationsolution in which the above disadvantages are avoided. The presentinvention is characterised in that the electrostatic coalescer isincorporated in and constitutes an integrated part of the separatorbody, as stated in the attached claim 1.

The dependent claims 2-5 indicate the advantageous features of thepresent invention.

The present invention will be described in further detail in thefollowing with reference to the attached drawings, where:

FIG. 1 shows an elementary sketch of a pipe separator in accordance withthe present invention.

FIG. 2 shows an enlarged part of the separator shown in FIG. 1 in thearea of the coalescer in a cross-section a) and a longitudinal sectionb).

The solution shown in FIG. 1 comprises a tubular separator body 1, aliquid seal 6, arranged downstream of the separator body, for the waterphase in the fluid (oil/water) that flows through the separator, adrainage device 7 with an outlet 8 for the separated water, a pigbattery 5, arranged upstream of the separator body in connection with awell head 9, a connection pipe 10 that connects the well head to theseparator body 1 and a transport pipe 11 for oil downstream of theseparator body. The special feature of the present invention is that acoalescer 4 is incorporated in the separator body 1 as an integratedunit. The coalescer is expediently arranged at a distance of between ⅓and ½ of the length of the separator body from the inlet of theseparator body. However, its location is not limited to this. FIG. 2shows in large scale, in cross-section and longitudinal section, thepart of the separator body in which the coalescer is incorporated. Asthe figure shows, the coalescer comprises an upper electrode 12 and alower electrode 13 that are enclosed in expediently insulating materialin the wall 14 of the separator body. The electrodes are designed tohave applied to them (not shown in further detail) an expedient voltage“V” (AC voltage) to create an electric field that contributes toincreasing the separation of water from the fluid (oil and water)flowing through the separator. As FIG. 1 shows, a cyclone 3 (or anotherexpedient gas/liquid separator) is arranged upstream of the separatorbody 1 to remove any gas from the fluid that is produced in the wells 9.The intention of removing the gas is to avoid it reducing the effect ofthe coalescer as the gas is a poor electrical conductor. Anotherintention is to prevent the formation of plug flow in the separator.

The method of operation of the separator solution in accordance with thepresent invention is otherwise as follows:

Fluid, i.e. gas, oil and water, that is produced is passed first to thecyclone 3, where the majority of gas is removed and passed on in aseparate pipe 9, possibly being reintroduced into the transport pipe 11after the separator.

The liquid phase, which may contain small amounts of gas, is introducedinto the separator body 1. Free water will separate quickly and form awater phase under the oil phase. The gas bubbles will collect in the topof the separator pipe and, depending on their concentration, form a freegas phase. When coarse separation has been completed (i.e. the waterphase on the bottom, the oil phase with small oil drops in the centreand possibly a thin gas phase on the top), the fluid will pass into theintegrated coalescer 4.

In the coalescer 4, a voltage drop will be created mainly over the oilzone because the water zone conducts current and the gas zone also hasgood conduction properties.

The voltage drop over the oil zone (alternating current) producesincreased drop coalescence and destabilises the oil/water interface. Thewater drops grow in size and will separate quickly after the fluid hasentered the pipe separator element 1 again.

In the separator element downstream of the coalescer, the coalescedwater drops will be separated out and collected in the collection unit7, where the water is drained out via the pipe 8. The oil will flow onpast the water seal 6 to the transport pipe 11.

The present invention as it is defined in the claims is not limited tothe example shown and described above. The separator may be providedwith two or more coalescers 4 arranged in series in the separatorelement 1. This may be particularly relevant for oils that are difficultto separate such as heavier oils.

The cyclone 3 may also be located in places other than the well head asshown in FIG. 1. It has proved expedient for the cyclone to be locatedin connection with equipment that causes high shear for the fluid asthis produces good separation conditions. However, it may also berelevant to locate the cyclone in close proximity to the separator'sinlet in situations in which the separator is located far from the wellhead.

1-5. (canceled)
 6. A pipe separator for separation of fluids, forexample separation of oil, gas and water in connection with theextraction and production of oil and gas from formations under the seabed, comprising an extended, tubular separator body (1) that has adiameter at the inlet and outlet ends that is mainly equal to orslightly greater than the diameter of the transport pipe to which theseparator body is connected, a separator device, expediently a cyclone(3), arranged upstream of the separator body for separation of any gaspresent and an electrostatic coalescer (4) arranged in connection withthe pipe separator, wherein the electrostatic coalescer (4) isincorporated in and constitutes an integrated part of the separatorbody.
 7. A pipe separator in accordance with claim 6, wherein a waterseal (6) is arranged downstream of the separator element (1) and adevice (7) is arranged in connection with the water seal for drainage ofthe water that is separated out in the separator element (1).
 8. A pipeseparator in accordance with claim 6, wherein the separator element (1)comprises two or more coalescers arranged in series.
 9. A pipe separatorin accordance with claim 6, wherein the cyclone (3) is arranged inconnection with a throttle valve that produces high shear for the fluid.10. A pipe separator in accordance with claim 6, wherein the cyclone (3)is arranged in close proximity to the inlet of the separator element(1).
 11. A pipe separator in accordance with claim 7, wherein theseparator element (1) comprises two or more coalescers arranged inseries.
 12. A pipe separator in accordance with claim 7, wherein thecyclone (3) is arranged in connection with a throttle valve thatproduces high shear for the fluid.
 13. A pipe separator in accordancewith claim 7, wherein the cyclone (3) is arranged in close proximity tothe inlet of the separator element (1).